Image data comprises a number of pixels having a number of components that contribute to defining the image, such as color and/or intensity. The image data generally includes various color or gray levels, which contribute to the color and/or intensity of each pixel in the image. Each pixel of the image is assigned a number or a set of numbers representing the amount of light or gray level for that color space at that particular spot, for example, the shade of gray in the pixel. Binary image data has two possible values for each pixel, black (or a specific color) (represented by the number “1”) or white (represented by the number “0”). Images that have a large range of shades are referred to as grayscale images. For example, grayscale images have an 8-bit value per pixel comprising 256 tones or shades of gray for each pixel in the image (gray level of 0 to 255). Grayscale image data may also be referred to as continuous tone or contone image data. The pixels in a color image may be defined in terms of a color space, typically with three values, such as RGB—R for red, G for green, and B for blue—or four values, such as CMYK—C for cyan, M for magenta, Y for yellow, and K for black.
The pixels may also be defined in terms of device independent space (e.g., when inputting image data, such as standard RGB (sRGB) or CIE L*a*b) or a device dependent space (e.g., when outputting image data, such as RGB or CMYK). When outputting image data to an output device (e.g., copier, printer, or multi-function device (MFD)), a percentage scale may be used to identify how much ink is employed for a print or copy job. Such information may typically be used for billing a customer for print or copy jobs. For example, some methods employ a billing strategy based on an estimated amount of ink or toner consumption; others bill customers based on a print mode selection (e.g., draft, standard, color, enhanced, etc.) of the output device. In dynamic print-job environments, because printing documents using black ink or toner is less expensive than using colored ink or toner, billing is often based on the amount of color content contained in the job to be printed. In order to bill customers for color printing, color detection is an important feature required in an image path. Color detection is used to analyze documents for presence of color as well as an amount of color in order to bill customers accordingly. Generally, the higher the presence and amount of color in a document, the higher the cost.
Some systems include counting the number of pixels in the image data of the document to be printed. For example, a number of binary pixels associated with the CMYK color planes may be counted to determine a pixel count for each category of color at the time of marking for output in the image path. Generally, with existing color detection and counting methods, a pixel will be labeled as color when the presence of any one of the C, M, and Y signals is detected. U.S. patent application Ser. No. 12/252,391 (published as Patent Application No. 2010/0100505 A1), filed Oct. 16, 2008 by the same Assignee (Xerox Corporation), which is hereby incorporated by reference in its entirety, proposes a way to count color pixels. In solid ink and ink jet products, however, it is desirable to render neutral gray objects with CMYK ink (e.g., create objects that appear gray to the human eye by using a particular combination of C, M, Y, and K, thus enabling higher image quality)). This could substantially decrease the appearance of graininess in large uniform gray areas, such as a gray fill or sweep. For billing purposes, it is not desirable to charge customer for color pixels that were (are) supposed to be gray. The above-referenced '505 publication, for example, has limitations in handling images that are converted to contone from rendered binary data.
In a typical multi-tier billing system for production printers, images are placed into different tiers based on the amount of color content on each page. Placing the image in the correct tier level is important both from the customer's, as well as the company's, perspective. Solid ink jet printer machines render neutral areas of an image with a combination of cyan, magenta, yellow, black (CMYK) toner/ink when printing or copying. This, however, creates problems in billing since these “gray” counts may be composed of color toners that mimic gray but are counted towards color.
This is because most existing billing systems are based on counting the number of color pixels in the C, M, Y planes, either simultaneously or separately, using a fixed offset to compensate for the composite black or gray areas. This (the fixed offset) sometimes causes the image to fall into a wrong tier level. For instance, a given pixel may be counted as a color pixel when the presence of any one of the C, M, and Y signals is detected—although it may actually be neutral gray. This increases the possibility of a page with composite black or gray to be classified as color, which is undesirable, because the color content results used to determine a billing strategy for a document may be skewed That is, the color classification may cause selection of a higher cost color billing strategy or a higher billing tier (selected from a multi-tier billing structure). Therefore, the customer may be billed for printing the document at a higher rate even though the output document reflects color pixels that are neutralized or gray. Vice versa, the page or document could be classified as neutral when it contains color. The billing strategy for a document in such a case could also be incorrect, and can result in the user being billed a lesser amount because of a selected lower billing tier. For example, a user or customer might not be billed even though the document contains a billable amount of very colorful pixels.
Other strategies have also been introduced to improve billing of documents. For example, U.S. patent application Ser. No. 12/962,298, filed Dec. 7, 2010 by the same Assignee (Xerox Corporation, which is incorporated herein by reference in its entirety), proposes a hybrid method of counting color pixels by making use of existing hardware in the image path. In one embodiment, the normalized minimum of the two counts, one count from the CIE L*a*b neutral page based counting and the other from the CMYK based counting, is used to derive the billing tier. Another embodiment is to simply use the number of color pixels detected in the CIE L*a*b space to determine the billing tier. The '298 application also proposes a method to perform area coverage based color pixel counting for the copy path. It uses the neutral pixel detection information obtained in CIE L*a*b space to control the counting of color pixels in rendered binary CMYK space.
While methods such that those above can be effective in dealing with composite gray pixels that are generated in the marking stage in solid inkjet systems, they may be limited in handling composite gray originals in the scanning process (e.g., due to the relative small context used in neutral pixel detection).
Accordingly, an improved system and method of determining the color content in a document to more accurately bill customers is desirable.